In a digital data transmission system employing amplitude and phase modulation, such as the 16-ary quadrature amplitude modulation (16-QAM), the performance of a receiver is an essential receiver function. Automatic gain control (AGC) provides for uniform amplitude of the received signals across the signal constellation space. The more accurate the control of the amplitudes of the received signals, the better the demodulation performance of the demodulation of the received signals into data symbols. A 16-QAM AGC receiver has used a 16-QAM symbol demodulator in combination with an AGC error detector for AGC. Particularly, the prior 16-QAM AGC receiver subsystems have used average weights across the entire signal constellation space as constituents of the generated AGC error signal. However, power variability of the received signals in the signal constellation space can produce suboptimal AGC when all of the constellation points are averaged. These and other disadvantages are solved or reduced using the invention.